Window coverings, such as honeycomb window shades, Venetian blinds, and Roman shades typically have a head rail and a window cover material, such as pleated fabric, a plurality of slats, or blind members, which are controlled by cords, whereby a pull cord coupled to the slats, blind members, or fabric can be adjusted to raise or open the window covering. The pull cord extends from a headrail and is manipulated by a user to adjust the position of suspension cords and to thereby adjust the position of the window cover material. One shortcoming of such pull cords is that they require peripheral members that distract from the window cover material and can lessen the aesthetic appearance of the window covering. In addition, pull cords also present a potentially dangerous situation in that they are of relatively long lengths and may be mishandled by certain persons, especially children, such that accidental choking or hanging may occur.
There have been various developments in window coverings that do not utilize a lifting cord with a cord lock. One such patent is U.S. Pat. No. 2,420,301, issued May 13, 1947 to Cusumano for “Venetian Blind” which utilizes a cone-shaped member with grooves and a coil spring. This window covering design includes a counterbalance to enable positioning of the blind slats as desired without a lock. Another attempt includes U.S. Pat. No. 2,324,536 issued to Pratt and titled “Closure Structure” and utilizes tapes and coil springs to raise and lower a blind in which the bottom bar and the slats ride in tracks as they move upwardly and downwardly.
One issue that has been presented in other so-called cordless window coverings is that as a window covering is raised, increasing amounts of the window cover material are gathered and supported on the bottom rail, thereby increasing the weight suspended by the suspension cord. One patent directed to addressing this problem is U.S. Pat. No. 5,133,399, issued to Hiller et al. and titled “Apparatus by Which Horizontal and Vertical Blinds, Pleated Shades, Drapes and the Like May Be Balanced for No Load Operation.” In this device, a variable, upwardly directed force is applied to the cord structure with the force being substantially equivalent at all times to the combined weights of the lower rail and the blind members supported on the lower rail when the lower rail is above its lowermost operative position. The apparatus for applying the force includes a conical member coupled to a constant force spring or a variable force leaf spring. Other patents include U.S. Pat. No. 5,482,100, issued to Kuhar and titled “Cordless, Balanced Venetian Blind or Shade with Consistent Variable Force Spring Motor.”
In one version, a variable force spring is wound on drums whereby spring force imparted to a coiled spring is transferred from one drum to another. With these variable force spring motors, the force exerted is at its greatest when the blind or shade is fully raised such that the cords are supporting most or all of the weight for the bottom rail and the window cover material. The spring force is at its lowest point when the window covering is fully lowered such that only the bottom rail is supported by the suspension cord. In another embodiment, a constant force spring is utilized with a friction imparting device to accommodate the variable weight of the window covering between the raised and lowered positions.
One shortcoming of the previous attempts, however, is the complexity of the designs in that a substantial number of interconnected parts are required. The present invention provides a cordless window covering and does so in a more efficient manner.